That's what I figured, but I was hoping I was wrong and mame was 'smart' enough to filter out system/game input differences like that, such that a search such as Rebelscum's would return the right info.
M'eh. This has been, er, "discussed" many times, and I'm sick of 'em now.*
Mame is designed to emulate the original chips and circuits (aka "hardware") as exactly as possible. What's "possible" depends on who's writing the game driver. If the original circuits had the wiring for an input, mame could/should include that info since that's what the circuits had, even if the original game player didn't have access to that "input", or if it wasn't actually hooked up to a device.
Including the info can cause confuses with mame users. Since mame is about emulating the original circuits, though, this isn't much of an issue to mame. Some of MameDev expressed that things like the button label, whether the button was hidden, or whether the input wasn't used at all (vs if the circuits were designed for it) was outside of mame's scope.
Which was one of the reasons controls.ini project was started; let mame coders worry about emulation, and keep the "it was 'fire' not 'shoot'", "the button wasn't wasn't usable by the player therefore it didn't exist"/"the original hardware had a hidden button wired up and so mame should document it" arguments elsewhere.
* My position:
Don't waste MameDev's time with minor issues that can be solved outside of mame; let them code what they want. It would be cool if mame had more complete documentation outside the chips & circuits, but not if it takes away from the hardcore coding the few people who volunteer to code mame.